1. Field of the Invention
The present invention relates to a CPP giant magnetoresistive head in which a sense current flows in the thickness direction (direction orthogonal to the film surface).
2. Description of the Related Art
Giant magnetoresistive elements (GMR elements) used as thin-film magnetic heads can be broadly divided into a current-in-plane (CIP) mode element, in which a sense current flows in the direction parallel to a surface of a layer constituting the element; and a current-perpendicular-to-plane mode element, in which a sense current flows in the direction perpendicular to a surface of a layer constituting the element.
The following description is disclosed in Japanese Unexamined Patent Application Publication Nos. 2001-266313, 2001-307307, 2002-289945, 2002-305338, and 2003-31871, and U.S. Pat. No. 5,739,987. FIG. 12 is a longitudinal sectional view showing an example of a structure of a CPP-GMR head using a known CPP-GMR element. A CPP-GMR head 100 includes a lower shield layer 110 extending in the x-direction shown in the figure; a lower nonmagnetic metal layer 120 on the middle of the lower shield layer 110 in the x-direction; a free magnetic layer 133, a nonmagnetic material layer 132, pinned magnetic layers 131, an antiferromagnetic layer 134, and an upper nonmagnetic metal layer 140, stacked in that order on the lower nonmagnetic metal layer 120; an upper shield layer 150 extending in the x-direction on the upper nonmagnetic metal layer 140; longitudinal bias layers 163 in contact with both sides of the nonmagnetic material layer 132 and part of one of the free magnetic layers 133; insulating layers 161 between the longitudinal bias layer 163 and the lower shield layer 110; insulating layers 164 between the longitudinal bias layer 163 and the upper shield layer 150; and bias underlying layers 162 interposed between the insulating layer 161 and the longitudinal bias layer 163.
In the CPP-GMR head 100 having the above-described structure, the sense current also flows through the antiferromagnetic layer 134 composed of, for example, PtMn. The antiferromagnetic layer 134 has a resistivity of about 200 μΩ·cm, which is significantly greater than those of the nonmagnetic metal layers 120 and 140, the free magnetic layer 133, and the pinned magnetic layer 131. Moreover, the antiferromagnetic layer 134 is required to have a large thickness in order to retain the antiferromagnetic property. When the distance between the lower and upper shield layers is about 600 Å, the thickness of the antiferromagnetic layer 134 should be about 200 Å. Such a thick antiferromagnetic layer 134 having a high resistivity increases the resistance of the antiferromagnetic layer 134, thus resulting in heat generation when the sense current flows. This heat generation (Joule heat) causes an increase in the temperature of the entire head, thereby degrading the high frequency characteristics and reliability of the head. Furthermore, the thick antiferromagnetic layer 134 results in difficulty in reducing the distance between the lower and upper shield layers and is disadvantageous for higher recording density. In a CIP-GMR head, since only about ten percent of the total sense current flows through an antiferromagnetic layer and no sense current flows through a shield layer, there is no problem as described above.
Consequently, an element not including the antiferromagnetic layer has recently been proposed. For example, in Japanese Patent Application No. 2004-47757, the present inventors have proposed a structure in which the pinned magnetic layer extends in the height direction longer than the nonmagnetic material layer and the free magnetic layer, and the length of the element in the height direction is greater than the track width of the element. This structure results in shape anisotropy in the direction parallel to the height direction of the pinned magnetic layer. Therefore, it is possible to stabilize the magnetization direction of the pinned magnetic layer in the uniaxial direction parallel to the height direction without the antiferromagnetic layer that fixes the magnetization direction of the pinned magnetic layer.
In the above-described structure proposed by the inventors, the pinned magnetic layer preferably retains the track width of the element and extends in the height direction. However, in recent years, since the GMR element has a very small track width of about 0.2 μm or less, it is difficult to form a pinned magnetic layer extending in the height direction while maintaining such a narrow track width under present circumstances, thus degrading the yield. There is a process for independently forming a pinned magnetic layer in the GMR element and a pinned magnetic layer behind the GMR element in the height direction (at a portion behind the element in the height direction). However, since the track width is very narrow, it is difficult to accurately align the pinned magnetic layer in the element with the pinned magnetic layer in the portion behind the element in the height direction.